1. Field of the Invention
The present invention relates to an angular velocity sensor which measures angular velocity by using a piezo-electric oscillation type gyro, and which can be used for measuring the movement of a moving body such as a vehicle, a ship, an airplane, a robot or the like. More specifically, the invention relates to an angular velocity sensor which is used for measuring rotational angular velocity for controlling the attitude of a vehicle, or for controlling the wheels and related portions of a vehicle, or which is used for a navigation system mounted on a vehicle. The invention further relates to a method of adjusting an angular velocity sensor by adjusting the output voltage of the angular velocity sensor.
2. Description of the Related Art
A conventional tuning fork-controlled gyro has, as shown in FIG. 21, two square poles formed on a vibrator 310, as well as driver piezo-electric elements 320 and detector piezo-electric elements 330 disposed at neighboring positions on the surfaces meeting at right angles and maintaining the same height. Furthermore, feedback piezo-electric elements 340 are disposed on the surfaces opposed to the driver piezo-electric elements 320 on the square poles of the vibrator 310. The driver and detector piezo-electric elements 320 and 330 disposed on the surfaces meeting at right angles on the square poles of the vibrator 310 help increase the amplitude of the vibrator 310 and increase sensitivity based upon the Coriolis force.
Even in the conventional tuning fork-type angular velocity sensor as shown in FIG. 20, a driver piezo-electric element 301 is adhered to the central portion on the front surface of the square member 300 and a detector piezo-electric element 302 is adhered to the central portion on the right-side surface of the square member 300.
When an AC signal is applied to the driver piezo-electric element 320 to vibrate the gyro, the piezo-electric element 320 expands and contracts and the square pole of the oscillator 310 bends and vibrates in a direction shown by an arrow in FIG. 21. With the conventional structure as shown in FIG. 22, however, an undesired signal is generates in the detector piezo-electric element 330 due to the expansion and contraction of the square pole of the vibrator 310 caused by the expansion and contraction of the driver piezo-electric element 320. This becomes a cause of offset noise of the gyro.
Moreover, a pair of piezo-electric elements work as capacitors whereby drive signals flow through the electrostatic capacitive coupling, resulting in the generation of offset noise.
FIG. 23 illustrates an angular velocity sensor which uses a square pole tuning fork-controlled piezo-electric vibration gyro. That is, two square poles 300 and 301 are supported by a base portion 310 via a support portion 340, and a driver piezo-electric element 320 and a detector piezo-electric element 330 are fastened to the surfaces meeting at right angles of each of the square poles 300. The support portion 340 may have the structure of a pin to support node of vibration as shown in FIG. 23, or the support portion may not be provided as shown in FIG. 24.
When the node is supported by a thin member such as a pin 340 having a circular shape in cross section as shown in FIG. 23, however, undesired vibration is generated at the support portion 340 particularly when the vibrator is out of balance due to dispersion introduced in the step of production, making it difficult to firmly support the vibrator.
When the vibrator is secured without using the support portion as shown in FIG. 24, furthermore, vibration leaks to a great extent and the vibrator cannot be efficiently vibrated.
Furthermore, the leakage of vibration affects the offset signal output from the sensor, and also the leakage of vibration that changes depending upon the temperature becomes a cause of temperature drift offset.